The detection of tumorous lesions in the breast has progressed from early observation and palpation procedures to a variety of somewhat sophisticated imaging systems. A consequence of these advances in tumor detection is the identification of suspect tumor at an early stage in its development. Generally, at such early stages the suspect tumor may be somewhat small. Rather than resort immediately to an open surgical resection upon such early detection, practitioners generally carry out a preliminary, minimally invasive biopsy procedure. Such preliminary biopsy approaches are of importance, inasmuch as statistically, only 20% of these small tumors will be found to be malignant. Tumors determined to be benign have been left in situ with no excision. Over one million of these biopsies are performed in the United States each year, the procedure providing for the removal of part or all the suspect tissue for pathology examination and diagnosis. See generally:                (1) Rosen, Paul Peter, “Rosen's Breast Pathology”, Lippincott-Raven Publishers, Philadelphia, 1997 pp 837-858.        
One of the minimally invasive options is needle biopsy which may be either fine needle aspiration (FNA) or large core. Fine needle aspiration (FNA) is a procedure in which a fine needle, for example, of 21 to 23 gauge, having one of a number of tip configurations, such as the Chiba, Franzeen or Turner, is inserted into the breast and guided to the tumor site. A vacuum is created and the needle moved up and down along the tumor to assure that it collects targeted cellular material. Generally, three or more passes will be made to assure the collection of sufficient sample. Then, the needle and tissue sample are withdrawn from the breast for analysis.
The resulting specimen is subject to cytologic assay. In this regard, cell structure and related aspects are studied. This analysis has been used to improve or customize the selection of chemotherapeutic agents with respect to a particular patient.
While a fine needle aspiration biopsy has the advantage of being relatively simple, there are some drawbacks associated with its use. With fine needle aspiration, there remains a risk of false-negative results, which most often occur in cases involving extremely fibrotic tumor. In addition, after the procedure has been performed there may be insufficient specimen material for diagnosis. Finally, with fine needle aspiration alone the entire area of suspect tissue is not removed. Rather fragmented portions of tissue are withdrawn which do not allow a more advanced pathological investigation.
This limitation also is observed with respect to large core needle biopsies. For a large core needle biopsy, a 14 to 18 gauge needle is inserted in the breast having an inner trocar with a sample notch at the distal end and an outer cutting cannula. Similar to a fine needle aspiration, tissue is drawn through a needle by vacuum suction. These needles have been combined with biopsy guns to provide automated insertion that makes the procedure shorter and partially eliminates location mistakes caused by human error or lesion displacement. Once inserted, multiple contiguous tissue samples may be taken at a time.
Samples taken during large core needle biopsies may be anywhere from friable and fragmented to large pieces 20 to 30 mm long. These samples may provide some histological data, unlike fine needle aspiration samples. However, they still do not provide optimum pathological information. For further information concerning needle biopsy procedures see the following:                (2) Parker, Steve H, “Needle Selection and Steriotatic Large-Core Breast Biopsy”, Percutaneous Breast Biopsy Eds. Parker, et al, Raven Press, New York, 1993 pp 7-14 and 61-79.        
A device, which is somewhere between a needle biopsy and open surgery, is referred to as the Advanced Breast Biopsy Instrumentation (ABBI). With the ABBI procedure, the practitioner, guided by appropriate imaging, removes a core tissue sample of 5 mm to 20 mm in diameter. While the ABBI has the advantage of providing a large tissue sample similar to that obtained from an open surgical biopsy, the cylindrical tissue sample is taken from the subcutaneous tissue to an area beyond the suspect tumor. For tumors embedded more deeply within the breast, the amount of tissue removed is considerable. In addition, while less expensive than open surgical biopsy, the ABBI has proven expensive compared to other biopsy techniques, and it has been noted that the patient selection for ABBI is limited by the size and location of the tumor, as well as by the presence of very dense parenchyma around the tumor. See the following publications:                (3) Parker, Steve H., “The Advanced Breast Biopsy Instrumentation: Another Trojan Horse?”, Am. J. Radiology 1998; 171:51-53.        (4) D'Angelo, Philip C., et al., “Sterotatic Excisional Breast Biopsies Utilizing The Advanced Breast Biopsy Instrumentation System”, Am. J. Surg. 1997; 174: 297-302.        (5) Ferzli, George S., et al., “Advanced Breast Biopsy Instrumentation: A Critique”, J. Am. Coll. Surg., 1997; 185: 145-151.        
Another biopsy approach has been referred to as the mammotome and the Minimally Invasive Breast Biopsy (MIBB). These devices carry out a vacuum-assisted core biopsy wherein fragments of suspect tissue are removed with an 11-14 gauge needle. While being less invasive, the mammatome and MIBB yield only a fragmentary specimen for pathological study. These devices therefore are consistent with other breast biopsy devices in that the degree of invasiveness of the procedure necessarily is counterbalanced against the need of obtaining a tissue sample whose size and margins are commensurate with pathology requirements for diagnosis and treatment.
A minimally invasive approach to accessing breast lesions wherein the lesion is partially removed or removed in its entirety for diagnostic as well as therapeutic purposes has been described in U.S. Pat. No. 6,277,083 by Eggers, et al., entitled “Minimally Invasive Intact Recovery Of Tissue”, issued Aug. 21, 2001. The instrument described includes a tubular delivery cannula of minimum outer diameter, the tip of which is positioned in confronting adjacency with a tissue volume to be removed. Following such positioning, the electrosurgically excited leading edge of a capture component is extended forwardly from the instrument tip to enlarge while electrosurgically cutting and surrounding or encapsulating a tissue volume, severing it from adjacent tissue. Following such capture, the instrument and the encaptured tissue volume are removed through an incision of somewhat limited extent.
An improved design for this instrument, now marketed under the trade designation EN-BLOC® by Neothemia Corporation of Natick Massachusetts, is described in U.S. Pat. No. 6,471,659 by Eggers, et al., entitled “Minimally Invasive Intact Recovery Of Tissue”, issued Oct. 29, 2002. The EN-BLOC® instrumentation includes a tubular delivery cannula of minimum outer diameter, the tip of which is positioned in confronting adjacency with the target tissue volume to be removed. Such positioning is facilitated through the utilization of a forwardly disposed precursor electrosurgical electrode assembly. Located within the interior channel of this delivery cannula is a capture component configured with five relatively elongate and thin leafs which are mutually interconnected at their base to define a pentagonal cross-sectional configuration. Each of these leafs terminates forwardly at a tip region with a transversely bent forwardly extending eyelet structure. Slidably extending through each eyelet is an electrically conductive pursing cable of a pursing cable assembly. The tips additionally extend through a guidance assembly at the forward region of the delivery cannula. When the capture component is driven forwardly by the drive tube of a drive assembly, these leafs deploy outwardly and forwardly at an initial angle of attack of 35° to 45° while the pursing cables are “played out” and establish an electrosurgical cutting arc. Thus, cable movement defines a cutting profile that is extending outwardly at the noted 35° to 45° while moving forwardly to define an initial cutting profile extending circumferentially about the targeted tissue volume.
Drive imparted to the capture component from the drive tube is developed ultimately from an electric motor within the drive assembly. Each of the five pursing cables extends from the leading edge portion of the capture component through the delivery cannula to a cable terminator component which is pulled forwardly by the cable as the capture component forward portion moves from its initial position substantially within the interior channel of the delivery cannula toward an intermediate position wherein the electrosurgically excited leading edge leaf forward regions and associated pursing cables have achieved an effective maximum diametric extent. At this juncture, about one half of the targeted tissue volume will have been circumscribed by the capture component. At this position, the slidable cable terminator component will engage a cable stop component or collar. Forward movement of the attached cable assembly will be halted and a pursing action will ensue at the electrosurgical cutting leading edge wherein the tip regions of the cables are drawn inwardly with mutually inwardly directed angles of attack until the leaf tip portions converge at a capture position defining a capture basket configuration or tissue recovery cage substantially encapsulating the entire target tissue volume. As this position is reached, the tensioned cables permit no further movement and a stall condition is recognized at the drive motor to terminate electrosurgical excitation of the cable-defined leading edge of the capture component. Drive then is removed from the capture component by reversing the directional output of the electric motor.
An advantageous feature of this form of drive assembly for the capture component resides in an arrangement where the noted cable stop component which engages the cable terminator component may be adjusted longitudinally to, in turn, vary the extent of the effective maximum diameter developed by the leading edge of the capture component. For example, the device can be configured to recover tissue specimens of 10 mm, 15 mm, 20 mm or greater effective maximum diametric extent. With the system, capture is positive, minimally invasive and the procedure is of short duration, for instance, requiring about 7 seconds to recover a 10 mm maximum effective diameter tissue sample. As another beneficial aspect, the shape of the resultant specimen is compact in that it will exhibit an aspect ratio of from about 1:1 to about 1:1.5 of effective diametric extent to longitudinal length. This is achieved by the initial 35° to 45° angle of attack of deployment to the intermediate position and the utilization of one pursing cable per leaf to essentially define a spherical encapsulation. In this regard, where stereotactic guidance and imagining is employed, the breast will be engaged with a compression plate such that recovery of elongate-shaped samples is undesirable.
Studies have been undertaken with respect to the employment of this instrument in the recovery of target tissue samples from very dense breast tissue including fibrous tissue. Such tissue will be infrequently encountered, however, a capability on the part of the instrument to recover samples from it is desirable. To emulate the dense tissue, porcine breast tissue was compressed with a clamping procedure. This provided a test medium which reproduced at least the mechanical properties of dense human breast tissue. The studies indicated that as the capture component leading edge reached the noted maximum effective diametric extent at its intermediate position or slightly beyond representing about a 50% to about a 75% deployment of the system, the system exhibited excessive motor currents which may reach levels indicating a stall characteristic. As the cable terminator engaged the maximum effective diameter defining cable stop to halt forward movement of the cables, their resultant stress load created these excessive motor currents which, in some cases, exceeded the control threshold representing a completion of capture. This potential capture failure phenomenon was observed to occur more frequently as the size of the maximum effective diameter increased, for instance, from 10 mm to 15 mm and above. However, the mechanical integrity of the capture component with pursing cables remained intact. While, as described in U.S. Pat. No. 6,471,659 (supra) the control system employs electronic masking to avoid shut-down due to frictional vagaries during early stages of the capture procedure, extension of such masking was deemed to be undesirable for safety-related reasons.